The Main Distortions in Encoded Video and Their Impact on Viewer Experience

04 Nov The Main Distortions in Encoded Video and Their Impact on Viewer Experience

In the world of audiovisual content distribution, ensuring a high-quality viewer experience is a constant challenge. The Quality of Experience (QoE) is affected by various distortions that can occur during video generation, processing, and broadcasting. These distortions influence not only visual perception but can also impact user satisfaction, affecting their loyalty to the platform or channel.
In this article, we’ll explore the primary distortions that occur throughout the video production and distribution chain, from content acquisition to final transmission. We’ll also see how tools like Video-MOS probes enable efficient detection, filtering, and correction of these issues.

1. Distortions Produced During Content Generation

Distortions that arise in the capture or creation of content are often linked to technical or artistic conditions during recording. Here are some of the most common examples:

• Excessive Brightness: Poor exposure control can lead to overexposed areas, causing important image details to be lost. While it can be an artistic choice, in excess, it negatively affects visual experience.
• Color Saturation: Oversaturated colors can appear artificial and tire the viewer. On the other hand, insufficient saturation can make images look washed out, reducing visual impact.
• Black Screen: Completely black frames often appear during programming changes or artistic transitions. However, if the black screen lasts too long, viewers might perceive it as a technical error.
• Static or Frozen Image: Common in sports events or statistics graphics, prolonged exposure to frozen images can frustrate viewers, especially if the quality of the static image is poor.
• Excessive Darkness: In certain genres like movies or documentaries, darkness can be a dramatic device. However, if it hinders proper scene interpretation, it negatively impacts audience perception.

2. Distortions Produced During Content Processing

Video processing, which includes compression, encoding, and transmission, is a common source of distortions. Some of the most relevant are:

• Macroblocking: This distortion appears as large pixel blocks, usually in fast-action or high-complexity scenes. It often results from excessive compression or an insufficient bit rate.
• Banding (Color Banding): Occurs when, instead of a smooth gradient, colors separate into well-defined bands. This often happens in areas with gradual color changes and is due to reduced color depth or video compression.
• Mosquito Noise: Appears as noise or artifacts around moving object edges or fine details, such as text or lines. This occurs when compression doesn’t allocate enough resources to these details, creating a visual “buzz.”
• Judder: This jumpy or irregular motion effect is common in quick pans or action sequences. It can be due to a low frame rate or synchronization issues during transmission.
• Color Bleeding: This distortion occurs when colors “bleed” or extend beyond their natural borders, blending into other areas. It is typically caused by poor color compression.
• Blurring Distortion: Blurring appears as a loss of sharpness and detail, resulting in a fuzzy image. It can result from excessive compression that removes critical details to save data space.
• Ringing: Shows up as visible artifacts around high-contrast edges, creating a “halo” effect around objects. This is especially disruptive in scenes with smooth backgrounds and defined edges.
• Aspect Ratio Distortion: Occurs when the image’s aspect ratio is incorrect, causing the image to appear stretched or squashed. This happens due to errors in aspect ratio signaling during transmission.

3. Distortions Produced During Broadcasting

Lastly, distortions can occur during content distribution and broadcasting. These distortions are often related to network issues or technical errors:

• Audio Signal Loss: An audio broadcasting failure can disrupt the viewer’s experience, even if the video continues to play correctly.
• Video Signal Loss: In this case, the viewer may still hear the audio, but the video stops or is lost entirely, creating a mismatch between the two elements.
• Frame Loss: When frames are lost during transmission, the video may appear choppy or jumpy, affecting playback smoothness.
• Block Loss: Refers to the loss of blocks of information within a frame, resulting in incomplete or pixelated images.
• Freezing: The video stops on a specific frame for an extended period, usually due to data loss in transmission.
• Signal Loss: Disconnection from the live stream URL can result in complete content loss, showing a black screen or error message.

How to Manage These Distortions with Video-MOS

While some distortions may be accepted by the audience as part of the content type or visual style, others can severely impact viewer experience. Video-MOS probes allow for measuring and classifying these distortions using a Mean Opinion Score (MOS) threshold, helping identify issues that most affect perceived quality.
Furthermore, Video-MOS can distinguish between typical distortions (expected in certain genres or formats) and unexpected distortions (indicating technical failures), enabling content providers to optimize service quality and efficiently correct issues.

Conclusion

Distortions in encoded video are an inevitable challenge in digital content distribution. However, with appropriate monitoring using tools like Video-MOS, it is possible to identify and correct issues that negatively impact QoE. By ensuring consistent visual quality, content providers can improve audience satisfaction and strengthen viewer loyalty.